GT31 Boardcrazy QLD

Anyone know where i can buy one online in Aus?

fletchk said...

Anyone know where i can buy one online in Aus?

Simon at Boardscrazy can be done on line.

yoyo said...

Salt , assuming you can change the recording on the I-gotU to one second it still outputs in gpx so the accuracy would probably be Garmin foretrex like at best which inflated speeds by up to a knot.

It would be interesting if someone who has both a i-gotU and a GT-31 did a comparison.

Here we go again,lets bash up Garmin again
I have never had this bull**** experience you keep coming up with Garmin, all I read is people having problems with GT-31 and GT-11 !!!!!

The Garmin display speed is calculated from the 'Doppler' data in a similar way to how the Navi does it. The difference is that the Navi GT GPS records this more accurate data to memory, the Garmin does not. Not only that, the Garmin records half as often and with less precision. While the data saved by the Garmin is not crap, it is some way below that recorded by the GT.
Memories are short. There were lots of threads about dead and dying Garmins a few years a go and endless threads about interface issues with com ports, serial to usb adapters, connection cradles and ongoing questions about how to set up and use them. While we still see some issues with the GT's, they seem to be less and less as the technology and the support system has matured .

No but if you send me one for review (You work for Garmin, right?) I will try it.

Looked up some specs on it:

-10,000 data points = no improvement. Not even in the same universe as Navi GT's with their huge storage on SD cards!
-IPX7 'waterproofing' = Joke. Same as old one. No improvement and not worth anything for windsurfing without extra protection. (Same as Navi GT)
-Update rate is listed a 1 second. This is twice as good as the old foretrex and same as Navi GT's. BUT! No mention of Speed Over Ground ('Doppler') recording so I assume it doesn't.= still no good to us for accurate speed measurement.
-Still uses .GPX file format which may limit the precision of trackpoints and may still have 'Grid Effect' = lousy precision for speed measurement compared with Navi GT's which use binary format with high level of precision saved to file.
-Uses AAA batteries which means a weak point for waterproofing = a step backwards from Foretrex 201 which had a 'sealed in' battery.
-Now has USB cable interface which should mean far faster and easier download of log file and better compatibility with Apple Mac and other operating systems. = useful improvement.

Many of us in the speed sailing community approached Garmin at various levels outlining our needs and requesting certain design updates/changes. We met with total apathy. This new model and redesign would have been a great opportunity for those features we need to be included. Nope! Obviously Garmin have no interest in selling their GPS units to the speed sailing community.

Wood Duck said...

Wood Duck said...

yoyo said...

Salt , assuming you can change the recording on the I-gotU to one second it still outputs in gpx so the accuracy would probably be Garmin foretrex like at best which inflated speeds by up to a knot.

It would be interesting if someone who has both a i-gotU and a GT-31 did a comparison.

Here we go again,lets bash up Garmin again
I have never had this bull**** experience you keep coming up with Garmin, all I read is people having problems with GT-31 and GT-11 !!!!!

"Wood Duck" is "Wood Duck"

I've sold 1000's of Garmins Handheld units.......as we all know you will be lucky to get an season out of the foretrex 201.
All the other Garmin Handhelds are consumer items.......i've sent many back for repair, failure rate is too high for an expensive item!

Stick with the Navi!!, the Navi casing may look antiquated.
Whats most important is the GPS internals & software.

As most windsurfers use the Navi....it is more talked about, most problems with the Navi are user related.

yoyo said...



And what was the source of your base line data?
Perhaps the Navi measured and included the side to side wanderings of your walk down the trail whilst the Garmin just assumed by trackpoint measurements that all those slight deviations didn't exist. In that case the Navi would be the most accurate and the Garmin underestimated the ACTUAL distance you walked by 10%

Errr... no, the NAVI was wrong, in the following way:

For the NAVI, the displayed distance was 10% different to the trackpoint distance when I analysed the track later on. The Garmin displayed distance matched the trackpoint distance.

Both our trackpoint distances were within 1% of each other, the problem was the displayed distance on the NAVI. I'd guess that the doppler distance calculation isn't set up properly for low speeds.

I was quite surprised, because I thought that the NAVI was the best GPS you could get in every respect, but it appears I was wrong.

Which begs the question: How is the display distance on the Navi calculated? Is it calculated from 'Doppler' data? If it is, (and I would not assume that) that could be an explanation of the difference.

Hmmmm OK yoyo you think what you like mate.

All I know is that:
The (surveyed) map, the garmin display, the garmin trackpoint log, and the NAVI trackpoint log all indicated a distance of 17.6 km.
The NAVI display, and the NAVI doppler distance log indicated 15.3km at the same point.

Draw your own conclusions.

It's odd that the difference is so significant (>10%). Mostly when speed sailing, the difference is more like 1%. This indicates to me that there is some low-speed filtering going on, which is ignoring speeds below a certain threshold. It also indicates that basing distance calculations off doppler values isn't the best way to do things. But what would I know

Herbylyn said...

...........but at this stage I would say that if you buy a Navi, then you should consider a Garmin as back up.

sorry to hear of your freeze up issues. I have only had one with a GT-31 (out of the 3 I have) and after resetting there it has not repeated.

The only way to go is to have two GT's. With any technology you need redundancy. (Murphy's law!) Right from the start I have used 2 GPS just because if I have a PB session I don't want to get home and find one has failed to record for whatever reason (water in the works, user error, flat battery, unit failure etc).
In fact I often carry 3 because I have two in my helmet (for best reception) and cant see them while I am sailing, so I wear a third on my arm.

Well i bought teh Photo Logger i-gotU GT-120 because it's water resistant and i paid 70 bux for a new one :)

U can tune it to 1 sec recording and lasts about 4hrs. I'll post my data .review and a link to it on google earth so u can check it out. Should be fine i reckon. It just doesn't have a screen so u need to upload data b4 u can see ur world record :)

Yeah sausage and Yoyo, I think the troubles may be over.. This morning when it turned itself off I updated to the Version B1123T from B1405X. Also formatted Lyns card 3 times. Only half charged it so if it did freeze it wouldn't take so long to flatten...__Be good if there was a hole where you could reset them__

Actually my backup Garmin Venture which I carry on mast and has big display stopped displaying, but when I came in and pressed the toggle it started up again.

the troubles were frustrating but I am still in the camp of the Navi. (fingers crossed)
This has been a good and interesting thread.

Yes you can download the GPX data and it comes with is own software if you choose to use it its pretty good.

Update: battery life approx 10hrs.
Water resistant- not reccomended for swimming etc so i'll just have to be awesome and never fall off my board.

I think its going to be fine.

One question:
how is the data from other devices any different. (Besides product features such as screens etc)

SirfIII chipset - check
1 second incriment recording- check

What else is there?>


Ill update this thread when i get some results, probably in 5 days.

Cheers

nebbian said...

Hmmmm OK yoyo you think what you like mate.

All I know is that:
The (surveyed) map, the garmin display, the garmin trackpoint log, and the NAVI trackpoint log all indicated a distance of 17.6 km.
The NAVI display, and the NAVI doppler distance log indicated 15.3km at the same point.

Draw your own conclusions.

It's odd that the difference is so significant (>10%). Mostly when speed sailing, the difference is more like 1%. This indicates to me that there is some low-speed filtering going on, which is ignoring speeds below a certain threshold. It also indicates that basing distance calculations off doppler values isn't the best way to do things. But what would I know

Nebbs congrats on the PBs yesterday.

But on the Garmin/Navi, I'd back the Navi everytime. Sure the survey may say 17.6km but how do you think they got that number in the first place? I'd bet London to a brick it was a park ranger using a Garmin Etrex years ago with it's rounded up trackpoint data.

When gps were first used for speedsailing the Dutch guys had to use 2 second periods for the max speed because the 1 sec was way to spiky on their Garmins Gekos. After noticing that my own Garmin speeds seemed to come in discrete steps I decided to do some tests myself and found that the trackpoints that the software showed was rounded up to the nearest 2.4m N-S and 1.85m E-W. After emailing and discussing with Manfred ****hs (GPS-Speed) Mal Wright (Realspeed) and Yann (GPS Action Replay ) it was clear that it was and issue with garmin rounding up the data it stored in their log and not the software. After many emails and phone calls to Garmin and several denials finally a tecky there confirmed that is exactly what Garmin do and they had no intention of changing as most user didn't need the accuracy we required.. although there were some models that stored the full data like the Edge which was promoted as a cycling unit so had similar requirement to speedsailing (speeds and distances).


Whilst this is not a true walking test it does show the differences in errors. Yesterday my gps was stationary for some time. For 12 minutes it had exactly zero movement. Yet the track point data says it moved 170m over those 720 seconds (and this was with the full, non rounded trackpoint 10X more accurate than the Etrex/foretrex etc). ~ 24cm error average each second. Meanwhile the doppler data was only 27m movement for the same time period or only 3.75cm error for each second recorded.

In the case of your walk. it probably took you about 3 hours. The accumulated error could easily be over 2 km if each measurement is 20cm more inaccurate than doppler.

In the image below the trackpoint speed error is black whilst the the green one is doppler.